Al toxicity mechanism in tolerant and sensitive rye genotypes

Rye (Secale cereale L.) plants have high tolerance to Al, and become unique tools to study Al-toxicity and tolerance mechanisms. To better understand if and how Al-induced root growth inhibition is related with root histological differentiation, nutrient balances and cell cycle dynamics, tolerant (AT6) and sensitive (AS6) rye lines were exposed for 24 h to 1.1 mM Al. After that period, half of plants were transferred to medium without Al, while the other group was maintained with Al for more 48 h. AS6 plants showed evident and irreversible root growth inhibition, decreases in water content, organic matter and carbohydrate reserves. Also, roots of this line showed greater increases in Ca levels and changes in anatomy (e.g. thickness). Data revealed that AS6 plants accumulate more Al in roots and leaves, suggesting more Al translocation to the shoots. The two lines responded differently to Al exposure in what concerns endodermis differentiation and cell cycle profile. The tolerant line shows a tendency to arrest in G0/G1 phase whereas the sensitive have a tendency to arrest in S phase. These data point to an arrest of cells in specific cell cycle phases, leading to eventual Al-induced cell cycle delay. Taken all together, data show that even short-term exposure to Al leads to root anatomical modifications that in combination with the cell cycle dynamic changes, may represent a plant strategy to cope with this stress.

► Al leads to root decrease in water content, organic matter and carbohydrates.
► Al exposure leads to an arrest of cell cycle in rye plants.
► Al-sensitive rye line shows Al translocation to the shoot.
► Al-tolerant line has mechanisms to prevent insufficient uptake of carbohydrates.
► Callose and endodermis seem to play complementary roles.